The objective of this project is to increase our understanding of the genetic basis of cellular differentiation. The elucidation of the genes involved and their action in cellular differentiation is essential to the understanding of embryonic development. The in vitro differentiation of neurons and myocytes, from their respective blast cells, is the experimental system on which the present investigation will be performed. The ability of cells from mutant embryos of Drosophila melanogaster to differentiate into neurons and myocytes will be investigated in culture. Known and induced embryonic lethal and female sterile mutations will be tested. The gene directed steps (unique and common) in the differentiative pathways of the two cell types wll be located. The time of gene action will be determined and related to the morphological stage at which this pathway is blocked. For genes which are common to both pathways, quantitative and qualitative differences in gene action in the two cell types will be investigated. Techniques for the isolation of these two cells types will be developed.